1. Field of the Disclosure
Aspects of the disclosure are related to adaptive positioning reference signal (PRS) for indoor location of a mobile device or terminal.
2. Description of the Related Art
Wireless communication systems have developed through various generations, including a first-generation analog wireless phone service (1G), a second-generation (2G) digital wireless phone service (including interim 2.5G networks) and third-generation (3G) and fourth-generation (4G) high speed data/Internet-capable wireless services.
More recently, Long Term Evolution (LTE) has been developed by the 3rd Generation Partnership Project (3GPP) as a radio access network technology for wireless communication of high-speed data and packetized voice for mobile phones and other mobile terminals. LTE has evolved from the Global System for Mobile Communications (GSM) system and from derivatives of GSM, such as Enhanced Data rates for GSM Evolution (EDGE), Universal Mobile Telecommunications System (UMTS), and High-Speed Packet Access (HSPA).
In North America, wireless communications systems, such as LTE, use a solution for Enhanced 911, or E911, that links emergency callers with the appropriate public resources. The solution attempts to automatically associate the caller, i.e., the caller's user equipment (UE), with a specific location, such as a physical address or geographic coordinates. Automatically locating the caller with high accuracy (e.g., with a distance error of 50 meters or less) and providing the location to a Public Safety Answering Point (P SAP) can increase the speed with which the public safety side can locate the required resources during emergencies, especially where the caller may be unable to communicate his/her location (e.g. does not know the location or is unable to speak adequately).
To locate a UE geographically, there are several approaches. One is to use some form of terrestrial radio location based on measurements made by a UE of signals transmitted by wireless network base stations and access points (APs) and/or based on measurements made by network elements (e.g., base stations and/or APs) of signals transmitted by the UE. Another approach is to use a Global Positioning System (GPS) receiver or Global Navigation Satellite System (GNSS) receiver built into the UE itself. Terrestrial radio location in a cellular telephony system may use measurements made by a UE of transmission timing differences between pairs of base stations or APs and may employ trilateration or multilateration techniques to determine the position of the UE based on two, or more commonly three or more, timing difference measurements.
One such terrestrial radio location method that is applicable to measurements of LTE base stations (referred to as eNodeBs or eNBs) and that is standardized by 3GPP in 3GPP Technical Specifications (TSs) 36.211, 36.305, and 36.355 is Observed Time Difference of Arrival (OTDOA). OTDOA is a multilateration method in which the UE measures the time difference between specific signals from several eNodeBs and either computes a location itself from these measurements or reports the measured time differences to an Enhanced Serving Mobile Location Center (E-SMLC) or to a Secure User Plane Location (SUPL) Location Platform (SLP), which then computes the UE's location. In either case, the measured time differences and knowledge of the eNodeBs' locations and relative transmission timing are used to calculate the UE's position.
Determination of an accurate location of a UE indoors may often be challenging. For example, signals from GPS or other GNSS satellites (e.g., for the Galileo, Glonass or Beidou GNSS systems) are usually attenuated and subject to multipath and are then often difficult for a UE to acquire and accurately measure when the UE is indoors. Signals transmitted from network base stations (e.g., LTE eNBs) may be received and measured by a UE in the case of a serving base station or other nearby base station but are typically also difficult for a UE to acquire and measure from a sufficient number of base stations to enable accurate location when a UE is indoors.
There is thus a benefit to enhancing positioning methods such as OTDOA to enable more accurate location indoors. Furthermore, any enhancements in indoor positioning accuracy for a method such as OTDOA may be used not only to accurately locate a UE that is making an E911 call but may also be used to locate a UE accurately for other purposes, for example, to locate a lost child, track a valuable asset (e.g. a car or truck) or guide a user to some indoor or outdoor destination. Therefore, the embodiments and examples described herein to improve location accuracy for a UE that is indoors or in a difficult outdoor environment such as a dense urban area may be used to locate the UE in the case of an emergency call or for other reasons.